1. Chapter 5 Energy

2. 5.1 What is Energy? Energy: the ability to do work or cause change
Work: Force * Distance
Work is done if a force makes something move.
In other words, when work is done, a change occurs.
When work is done and change occurs, energy moves from one place to another or changes form.

3. Two Types of Energy
All forms of energy fall into two types: kinetic and potential.
Potential energy: energy that is stored; also energy that is due to position
Kinetic energy: energy that is in motion; also depends on the mass and speed of an object

4. Energy Analogy
Money can be stored and converted into a variety of forms, like:
Cash (bills and coins), check, credit card, bank account.
Energy can also be stored and converted into different forms
Different energies are just different forms of the same thing: ENERGY

5. Converting Kinetic and Potential Energies
One energy form can transfer into other energy forms.
Example: a swinging pendulum (shown on next page)

7. Potential Energies There are many types of potential energies:
Chemical
Nuclear
Elastic
Gravitational

8. Potential: Chemical Energy
Chemical Energy: energy stored in the bonds of atoms and molecules.
Examples: food, coal, natural gas, and paper all contain chemical energy.
Calorie: food energy / 1g (fat=9C, carbs/protein=4C)

9. Potential: Nuclear Energy
Nuclear energy: energy stored in the nucleus of an atom.
Examples: Stars, uranium (power plants), plutonium (weapons).
Mass transfers into energy with fusion!

10. Potential: Elastic Energy
Elastic Energy: energy stored in objects that can be compressed or stretched
Examples: stretched rubber band, a compressed spring

11. Potential: Gravitational Energy
Gravitational Energy: the energy stored in objects due to mass & position above Earth.
Examples: water on top of a waterfall, airplane
GPE is calculated by the equation: GPE= mGh=mass kg*acceleration Gravity*height m
Unit for GPE is Joules!
Acceleration due to gravity = G = 9.8m/s2

12. GPE Example 1 GPE: Mass * 9.8 m/s2 * Height
A 250 kg boulder is sitting on the edge of a cliff that is 60m high. GPE=mGh
GPE = 60m * 9.8m/s/s * 250kg
GPE = Joules

13. GPE Example 2 GPE: Mass * 9.8 m/s2 * Height
A 10 kg brick is sitting on a platform that is 15 meters high. GPE?
GPE = 10kg * 9.8m/s/s * 15m
GPE = 1470 Joules

14. GPE Example 3 GPE: Mass * 9.8 m/s2 * Height
An 8 kg binder is sitting on a desk that is 1.5 meters high. GPE?
GPE = 8kg * 9.8m/s/s * 1.5m
GPE = Joules

15. Kinetic Energies Kinetic energy is the energy of motion.
It can be calculated with the equation:
½ * mass * (velocity)2
There are many types of kinetic energies:
Radiant
Thermal
Electrical
Mechanical
Sound

16. Kinetic Energy Calculation
Equation: KE = ½ * mass * (velocity)2 A car whose mass is 1000 kg moves at a speed of 20 m/s. Find the kinetic energy KE = ½ (1000kg) x (20m/s) x (20m/s) KE = ½ (1000) (400) = 200,000 J

17. Kinetic: Radiant Energy
Radiant energy: the energy that travels in electromagnetic waves.
Examples: radio wave, microwave, infrared, visible light, ultraviolet light, x-ray, gamma ray
This is sometimes referred to as electromagnetic energy.

18. Kinetic: Thermal Energy
Thermal Energy: energy caused by the internal vibration of atoms or molecules.
Examples: fire, or a warm slice of pizza

19. Kinetic: Electrical Energy
Electrical Energy: energy from the movement of electrons.
Examples: lightning, electricity

20. Kinetic: Mechanical Energy
Mechanical energy: energy occurring when an object is in motion.
Mechanical energy is also the sum of kinetic and potential energies.
Examples: moving water, biking

21. 5.1 NRG Analysis: Date___ Name_____________Hr__
Copy / answer in sentences. Show all work.
Explain if objects can have kinetic and potential energies at the same time.
Explain how kinetic energy of trucks can increase without changing their speed.
Find KE: mass=0.06kg, v=50m/s
Find GPE: mass=80kg, h=5m

22. Law of Conservation of Energy
Law of Conservation of Energy: states that energy cannot be created or destroyed; it transfers from one form to another.
The total amount of energy in the universe does not change.

23. Energy Conversions Energy transfers from one form to another.
Most energy in the universe is converted into thermal energy due to friction.
Examples:
Your body will convert chemical energy from food into what other types?
Using a blow dryer will convert electrical energy into what other types?

24. Explain the NRG Conversion
Energy begins in the sun as NUCLEAR.
Nuclear energy transfers into THERMAL and RADIANT.

25. NRG Conversion Continued
Radiant energy enters Earth’s atmosphere.
Plants store radiant energy into CHEMICAL ENERGY.

26. NRG Conversion Continued
Coal, a non-renewable energy source, provides 45% of the electrical energy in the U.S.
What other forms of energy could we use to produce electrical energy?

27. Explain the Conversions

28. 5.2 Law Analysis: Date___ Name_____________Hr__
Copy / answer in sentences. Show all work
How does friction affect mechanical NRG?
Explain which has more potential energy, a car on a mountain or on a hill.
A swing PE is 200J at its highest point & 50J at lowest. What is KE at lowest point?